1、Designation: D7941/D7941M 14Standard Test Method forHydrogen Purity Analysis Using a Continuous Wave CavityRing-Down Spectroscopy Analyzer1This standard is issued under the fixed designation D7941/D7941M; the number immediately following the designation indicates theyear of original adoption or, in
2、the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes contaminant determination infuel-cell-grade hydrogen as s
3、pecified in relevant ASTM andISO standards using cavity ring-down spectroscopy (CRDS).This standard test method is for the measurement of one ormultiple contaminants including, but not limited to, water(H2O), oxygen (O2), methane (CH4), carbon dioxide (CO2),carbon monoxide (CO), ammonia (NH3), and f
4、ormaldehyde(H2CO), henceforth referred to as “analyte.”1.2 This test method applies to CRDS analyzers with one ormultiple sensor modules (see 3.3 for definition), each of whichis designed for a specific analyte. This test method describessampling apparatus design, operating procedures, and qualityco
5、ntrol procedures required to obtain the stated levels ofprecision and accuracy.1.3 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the
6、 other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health pract
7、ices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D4150 Terminology Relating to Gaseous FuelsD5287 Practice for Automatic Sampling of Gaseous FuelsD7265 Specification for Hydrogen Thermophysical PropertyTablesD7606 Practice for Sa
8、mpling of High Pressure Hydrogenand Related Fuel Cell Feed GasesD7649 Test Method for Determination of Trace CarbonDioxide,Argon, Nitrogen, Oxygen and Water in HydrogenFuel by Jet Pulse Injection and Gas Chromatography/Mass Spectrometer AnalysisD7653 Test Method for Determination of Trace GaseousCon
9、taminants in Hydrogen Fuel by Fourier TransformInfrared (FTIR) Spectroscopy2.2 ISO Standards:3ISO/DIS 14687-2 Hydrogen fuelProduct specificationPart 2: Proton exchange membrane (PEM) fuel cellapplications for road vehiclesISO/DIS 14687-3 Hydrogen fuelProduct SpecificationPart 3: Proton exchange memb
10、rane (PEM) fuel cellapplications for stationary appliances2.3 U.S.-Specific Standards:SAE J2719-2011 (2011) Hydrogen Fuel Quality for FuelCell Vehicles42.3.7 California Code of Regulations, Title 4, Division 9,Chapter 6, Article 8, Sections 4180-4181 Hydrogen fuelquality requirements5Environmental P
11、rotection Agency 40 CFR: Protection of theEnvironment, Appendix B to Part 136 Definition andProcedure for the Determination of the Method DetectionLimit63. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, referto Terminology D4150.3.2 Acronyms:3.2.1 AIST, nNational
12、 Institute of Advanced IndustrialScience and Technology1This test method is under the jurisdiction ofASTM Committee D03 on GaseousFuels and is the direct responsibility of Subcommittee D03.14 on Hydrogen andFuel Cells.Current edition approved June 1, 2014. Published July 2014. DOI: 10.1520/D7941_D79
13、41M-142For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from International Organization for Standard
14、ization (ISO), 1, ch. dela Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http:/www.iso.org.4Available from SAE International (SAE), 400 Commonwealth Dr., Warrendale,PA 15096-0001, http:/www.sae.org.5Available from the California Office of Administrative Law, 300 Capitol Mall,Suite 1250, Sacram
15、ento, CA 95814, http:/www.oal.ca.gov/ccr.htm.6Available from United States Environmental ProtectionAgency (EPA), WilliamJefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20004,http:/www.epa.gov.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA
16、19428-2959. United States13.2.2 CRDS, ncavity ring-down spectroscopy3.2.3 IR, ninfrared3.2.4 kPa, nkilopascal3.2.5 LDL, nlower detection limit3.2.6 MSDS, nmaterial safety data sheet3.2.7 NIST, nNational Institute of Standards and Technol-ogy3.2.8 NPL, nNational Physical Laboratory3.2.9 ppb, nparts p
17、er billion v/v3.2.10 ppm, nparts per million v/v3.2.11 PTB, nPhysikalisch-Technische Bundesanstalt3.2.12 psig, npounds per square inch (gauge)3.2.13 slpm, nstandard liters per minute3.2.14 v/v, nvolume/volume ratio3.2.15 VCR, na type of compression gas fitting3.3 Additional DefinitionsThe “sensor mo
18、dule” consistsof the optical system (CRDS mirrors, reference cell, one ormore lasers, and other optical components), the detector, andthe internal gas handling components (gas lines, filters, andregulators). The complete instrument, including controlelectronics, can contain a single sensor module or
19、 multiplesensor modules.4. Summary of Test Method4.1 This test method provides a procedure for the samplingof trace contaminants contained in fuel-cell-grade hydrogenand subsequent measurement using cavity ring-down spectros-copy (CRDS). Instrument and sampling system configurationsfor sample pressu
20、res ranging from ambient to high pressure(defined as 960 kPa 125 psig) are described.5. Significance and Use5.1 Proton exchange membranes (PEM) used in fuel cellsare susceptible to contamination from a number of species thatcan be found in hydrogen. It is critical that these contaminantsbe measured
21、and verified to be present at or below the amountsstated in SAE J2719, ISO 14687-2 and ISO 14687-3 to ensureboth fuel cell longevity and optimum efficiency. Contaminantconcentrations as low as single-figure ppb for some species canseriously compromise the life span and efficiency of PEM fuelcells. T
22、he presence of contaminants in fuel-cell-grade hydro-gen can, in some cases, have a permanent adverse impact onfuel cell efficiency and usability. It is critical to monitor theconcentration of key contaminants in hydrogen during theproduction phase through to delivery of the fuel to a fuel cellvehic
23、le or other PEM fuel cell application. In ISO 14687-2 andISO 14687-3, the upper limits for the aforementioned contami-nants are specified. Refer to SAE J2719 and the CaliforniaCode of Regulations (see 2.3) for example specific national andregional requirements. For hydrogen fuel that is transporteda
24、nd delivered as a cryogenic liquid, there is additional risk ofintroducing impurities during transport and delivery opera-tions. For instance, moisture can build up over time in liquidtransfer lines, critical control components, and long-termstorage facilities, which can lead to icing up within the
25、systemand subsequent blockages that pose a safety risk or theintroduction of contaminants into the gas stream upon evapo-ration of the liquid. Users are reminded to consult PracticeD7265 for critical thermophysical property such as the ortho/para hydrogen spin isomer inversion that can lead to addit
26、ionalhazards in liquid hydrogen usage. In addition to this testmethod employing CRDS, test methods such as D7649 (carbondioxide, argon, nitrogen, oxygen and water) and D7653 (IRactive species) are used to measure impurities in hydrogen fuel.6. Apparatus6.1 The analyzers used to measure impurities wi
27、th referenceto the development of this test method are based on CRDS.CRDS is an optical spectroscopic technique that enablesmeasurement of absolute optical extinction by samples thatscatter and absorb light. Based upon the optical extinction or“ring-down” rate, a determination of the analyte concent
28、rationcan be made. See Appendix X1 for a detailed explanation onthe principles upon which CRDS is based.6.2 Measurement Sequence6.2.1 A tunable laser emits a directed beam of light energythrough an ultra-high reflectivity mirror into the absorption cell(cavity). The sample gas passes through this ce
29、ll either via theuse of a vacuum pump for samples under 170 kPa 10 psig orunder pressure from sources in excess of 170 kPa 10 psig,regulated to between 170 and 960 kPa 10 and 125 psig.6.2.2 High sensitivity is attained by reflecting the laser lightmany times through a sample gas contained between tw
30、ohighly reflective mirrors; thereby, a path length as high asmany kilometers through the sample is obtained.6.2.3 A detector such as a photodiode senses the initialphoton flux at the output of the cavity. Once a preset level oflight intensity is detected, the light source is shuttered ordiverted fro
31、m the cavity, and the light intensity is measuredover time.6.2.4 On each successive pass through the cell, a smallamount of light or ring-down signal emits through the secondmirror and is measured by the photodiode detector.6.2.5 Once the light “rings down,” the detector achieves apoint of zero ligh
32、t intensity within a few hundred microsecondsand the measurement is complete.6.2.6 Two measurement sequences are required to effect ameasurement of concentration:6.2.6.1 On-peak MeasurementThe laser is tuned to awavelength at which the analyte absorbs light. The wavelengthof choice depends on the an
33、alyte, the targeted concentrationrange, and potential interference from other molecules presentin the sample. Suitable wavelengths for certain molecule cancommonly be determined by using spectroscopic databasessuch as HITRAN. The exact wavelength used for each analyteis generally considered a trade
34、secret by the manufacturer.6.2.6.2 Off-peak MeasurementThe laser is tuned to awavelength at which the analyte does not absorb light. Thewavelength of choice depends on the analyte, the targetedconcentration range, and potential interference from othermolecules present in the sample. As before, suita
35、ble wave-lengths can be determined by consulting spectroscopic data-bases such as HITRAN. The exact wavelength used for theD7941/D7941M 142off-peak measurement of each analyte is considered a tradesecret by the manufacturer, but it is generally in close proxim-ity to the on-peak wavelength. In a gas
36、 of consistent analyteconcentration, an off-peak measurement is required only occa-sionally; however, it is recommended that an off-peak mea-surement is performed at least once per month. In samples withrapidly changing gas composition or analyte concentrations, anoff-peak measurement may be perform
37、ed as frequently asevery few minutes. The frequency of off-peak measurementdoes not affect the accuracy of the final measurement.6.2.7 The on-peak and off-peak measurements are used tocalculate the concentration of the analyte in the sample gas asper a variation of the Beer-Lambert Law relating the
38、extinctionof light to the absorbance of the material through which thelight is travelling.6.3 Details concerning specific instrument configurationsfor a range of sample pressures can be found in Section 9.6.4 A full description of the CRDS technique can be foundin Appendix X1.7. Hazards7.1 High-pres
39、sure gases.WARNING Improper handling of compressed gas cylin-ders containing air, hydrogen, or inert gases such as nitrogen orhelium can result in explosion. Rapid release of hydrogen orinert gases can result in asphyxiation. Hydrogen is a potentialfire hazard. Compressed air supports combustion.7.2
40、 Hydrogen7.2.1 Potential explosion hazard.7.2.2 Purge with inert gas before oxygen service.8. Equipment, Materials, and Supplies8.1 Equipment8.1.1 CRDS analyzer consisting of laser source(s), samplecavity, photodiode detector, reference gas cell, and internal gashandling components (gas lines, parti
41、cle filters, and regulatorsto maintain a constant pressure), which constitute each sensormodule, as well as control electronics.8.1.2 Electrical and fiber optic cables to connect the controlelectronics and the laser source with each sensor module, if thesensing modules are provided as separate units
42、.8.1.3 Gas sample lines made from appropriate material(stainless steel recommended) with a diameter of at least 6 mm0.25 in. from the sample extraction point to the analyzer inletand the analyzer outlet to the vent or vacuum pump.8.1.4 A vacuum pump for low pressure samples (see 9.1.1)which can reac
43、h a pressure of approximately 1 Torr or less.8.2 Materials and SuppliesDry inert gas (e.g. nitrogen orclean dry air) as purge gas for installation of the analyzer.9. Sampling, Test Specimens, and Test Units9.1 Sampling9.1.1 For those CRDS instruments that can accept samplepressures from ambient up t
44、o 960 kPa 125 psig, a vacuumpump is required for sample pressures below 170 kPa 10psig. The analyzer may be used in the absence of a vacuumpump for sample pressures between 170 and 960 kPa 10 and125 psig. Samples with a pressure in excess of 960 kPa 125psig shall be regulated down to a pressure acce
45、ptable for theCRDS instrument before introduction to the inlet. Exceedingthe maximum allowable pressure may damage the instrument.Consult the manufacturer for required sample pressure condi-tions. CRDS analyzers configured exclusively for use atpressures above 170 kPa 10 psig cannot be used for lowe
46、rpressure samples even with addition of a vacuum pump.9.1.2 Commonly available CRDS instruments contain ap-propriate particle filtration inside the internal gas handlingcomponents; further filtration is generally not required unlessspecified by the manufacturer for special analytes and sampleconditi
47、ons9.1.3 To connect gas lines to the instrument, VCR fittingsare recommended. When making connections, always use anew gasket (nickel or stainless steel gaskets are recom-mended).9.1.4 For the measurement of most common analytes (e.g.H2O), sample lines and wetted components shall be of stainlessstee
48、l construction, ideally with electro-polished surface finish,free from particulate and other contamination such as oils andother hydrocarbons. Certain analytes may require alternativematerials or surface treatments, or both, to optimize samplingconditions. Contact an appropriate vendor for further a
49、dvice.9.1.5 Switching valves shall be constructed with a stainlesssteel diaphragm type and with the surface area of valves andother wetted components kept to a minimum, avoiding anydead volume. Surface treatments for the wetted surfaces whenavailable to minimize the absorption of impurities. Contact anappropriate vendor for further advice. Sample line lengthshould be minimized and “dead-legs” avoided, preventingdiffusion of contamination from unswept surfaces. Refer toPractices D5287 and D7606 for further sampling guidance.9.1.6 S
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